crystal-lang/crystal

Crystal is a compiled programming language designed to feel like Ruby, one of the most developer-friendly scripting languages, while running with the speed and efficiency of compiled C programs. The README summarizes the goal simply: "We love Ruby's efficiency for writing code. We love C's efficiency for running code. We want the best of both worlds." The language achieves this through several design choices. It looks syntactically very similar to Ruby, so developers familiar with Ruby can read and write Crystal code without a steep learning curve. However, unlike Ruby (which figures out types at runtime), Crystal uses static type-checking, it verifies that variables and functions are used consistently before the program even runs, catching a whole class of bugs at compile time. Crucially, you usually do not have to write type annotations everywhere; Crystal's compiler infers types automatically from how you use things. The resulting program compiles to native machine code, making it significantly faster at runtime than interpreted languages. Other notable features include the ability to call C libraries directly by writing bindings in Crystal itself (without needing a separate C file), and compile-time code generation to reduce repetitive boilerplate. Crystal supports full object-oriented programming. You would reach for Crystal when you want Ruby's pleasant syntax and rapid development experience but need your application to run much faster, for example in web APIs, background processing, or command-line tools where performance matters. It runs on Linux, macOS, and Windows (ARM and x86-64). The compiler is itself written in Crystal.